1. Field of the Invention
The present invention relates to the field of display device manufacture, and in particular to an ultraviolet light based cleansing method and cleansing device.
2. The Related Arts
A flat panel display has various advantages, including thin device body, low power consumption, and being free of radiation, and is thus widely used. The flat panel displays that are currently available generally include liquid crystal displays (LCDs) and organic light emitting displays (OLEDs).
Referring to FIG. 1, a conventional liquid crystal display generally comprises: a thin-film transistor (TFT) substrate 302, a color filter (CF) substrate 304 that is opposite to and is bonded to the TFT substrate 302, and a liquid crystal layer 306 interposed between the TFT substrate 302 and the CF substrate 304. The TFT substrate 302 drives the liquid crystal molecules of the liquid crystal layer 306 to rotate in order to display a corresponding image.
The conventional organic light emitting displays are classified according to the method of driving applied and include passive-matrix organic light emitting diode (PMOLED) and active-matrix organic light emitting device (AMOLED), wherein, as shown in FIG. 2, the AMOLED generally comprises: a substrate 502, a TFT 504 formed on the substrate 502, and an organic light-emitting diode 506 formed on the TFT 504. The TFT 504 drives the organic light-emitting diode 506 to emit light in order to display a corresponding image.
In a manufacturing process of the substrate, cleansing operations take 30%-40% of the total workload and the requirement for cleanness is extremely severe. Heretofore, there are generally two types of fine cleansing technique, one being dry cleansing technique and the other being wet cleansing technique. The wet cleansing is further divided into chemical cleansing and physical cleansing. The currently available chemical cleansing cannot meet the requirements and the shortcoming of the wet cleansing is the use of a great amount of pure water and toxicant chemical solvents in a cleansing operation, this readily resulting in hazards to the operators and environmental pollutions.
Ultraviolet (UV) light surface cleansing techniques are non-contact high-cleanness dry surface treatment techniques, of which the feature is the cleanness after the cleansing can achieve an atomic grade and which uses light and gas to completely remove all sorts of organic substances attached to a glass surface. Since no direct contact with the surface is made, there is no damage to the substrate surface. Further, no environmental pollution is caused.
The general principle of ultraviolet light cleansing is that an UV light source emits light waves having wavelengths of 185 nm and 254 nm, which carry extremely high energy. When the photons are applied to a surface of an object to be cleansed, due to the fact that most of the hydrocarbons have relatively high absorbability of ultraviolet light of 185 nm wavelength and can be decomposed into ions, free atoms, excited molecules and neutrons after absorbing the energy of the 185 nm wavelength ultraviolet light; this is generally referred to as photosensitization. Oxygen molecules contained in the atmosphere, after absorbing the 185 nm wavelength ultraviolet light, will also generate ozone and atomic oxygen. Ozone has strong absorption of the 254 nm wavelength ultraviolet light and ozone will further decompose into atomic oxygen and oxygen gas, of which the atomic oxygen is extremely active so that being acted on thereby, the decomposed components of carbons and hydrocarbons on the surface of the object can be combined to form volatile gases: carbon dioxide and steam to escape from the surface thereby completely eliminating carbons and organic contaminants attached to the surface of the object.
In the conventional OLED and low temperature poly-silicon (LTPS) techniques, equivalent ultraviolet (EUV) cleansing applied in a TFT manufacture process uses ultraviolet light of 172 nm wavelength. During the cleansing process, the ultraviolet light irradiating a metal electrode causes excitation of electrons, leading to a potential difference between metal patterns. When the potential difference exceeds the breakdown voltage of the patterns, a circuit breakdown may result, leading to un-repairable damage and thus affecting product yield rate.